Methods of attempting to substantially seal or otherwise reduce the permeability of a matrix such as concrete, rock or soil are known. For example, regular cement based suspension grouts can be introduced into voids, opens spaces and pore spaces around a mine shaft in order to attempt to seal fissures or reduce the permeability of unconsolidated sand or soil around the shaft, thereby limiting liquid inflow into the shaft.
Typically, a volume of grout or sealing composition product is transported to the site to be treated and applied to the passage or passages requiring sealing to prevent water inflow. Application typically involves pumping of grout to the passage or passages. Sealing composition which is generally premixed prior to delivery of the site often provides less than satisfactory results in terms of preventing or reducing water inflow. For example, injection or introduction of a cement based grout, known to have suitable properties in sealing passages, can cause hydrofracturing if applied to an unconsolidated matrix such as sand or sandstone. This can create seams of grout within the matrix, leaving sections of unconsolidated matrix on either side of the created seams. Such an application has minimal impact on reducing the ability for water to pass through the matrix and hence into a shaft that has been sunk through the matrix.
There is also difficulty in use of premixed grouts in that setting time cannot be controlled or varied either at all or with any reliable degree of accuracy. This is detrimental in that known premixed grouts are generally capable only of providing a “one size fits all” sealing solution. Since there is such a wide range of conditions that can be experienced when seeking to limit permeability of a matrix so as to limit liquid inflow, a ‘one size’ approach to all types of inflow problems is inherently unsuitable.
Traditional and pre-mixed cement and bitumen based grouts can additionally fail to adequately penetrate the passage or passages to be sealed. At least part of this failure can be attributed to the sealing composition simply failing to penetrate through the matrix to a required depth. Rate of setting of the sealing composition can also affect whether or not the sealing composition is able to adequately prevent or practically reduce water inflow.
For example, it is desirable when applying a grout to reduce permeability in a sand formation, that the grout can be able to permeate a suitable distance through the formation prior to setting. If setting occurs prematurely, the grout is unable to adequately penetrate the matrix and create sufficient adhesion of particles in the matrix to form an effective seal to water inflow.
Applicant's earlier patent AU 739427 utilises a composition which includes latex and wherein viscosity of the composition is increased with rate of shear as the composition penetrates into the passage. Whilst this can assist in controlling excessive grout spread within the matrix and help to ensure that the bulk of the grout remains within the target zone of the matrix, it still presents a somewhat generic approach to controlling set times of the grout once introduced into the passage. Further, set time of the grout cannot be regulated or varied with any degree of reliability to accommodate, for example, specific needs or requirements of the application at hand.
Another known method of preventing or limiting water inflow into an excavation in a ground formation is the method of ground freezing. This method is often the preferred method of ground support in vertical shaft construction. The method utilises water in situ in pore spaces of the ground formation and freezes it so that the water acts as a bonding agent, fusing together particles of soil or rock to create a solid mass with substantial impermeability. Whilst the ground is frozen, a concrete liner is usually constructed about the path of the shaft.
Proper execution of this method, particularly at depth, is complex and requires substantial capital outlay. After freezing and construction of the concrete liner and before the ground is permitted to thaw, absolute water tightness must be established in the concrete liner. If it is not water tight, seepage can dissolve matrix from behind the shaft lining, increasing the leakage path and ultimately flooding the mine. Salt mines in particular are known to be susceptible to this due to the salt dissolving and mines have been lost in this manner.
These aforementioned problems are also applicable and indeed may be more pronounced if it is desired to limit or reduce permeability of a matrix so as to reduce or limit flow of gas. For example, in a hydraulic fracturing (hydrofracturing) operation to extract hydrocarbon gas reserves from a reservoir, it may be desirable to limit the permeability of sections of ground surrounding the wellbore so as to prevent undesirable or disadvantageous flow of gas. It may also be desired to seal passages or pore spaces in a ground formation to seal in hydrocarbon or other gases in oil and gas seams. Known methodologies for reducing permeability of the ground to prevent or limit this have thus far been found to be largely ineffective or unreliable. In view of the fact that there is ever increasing reliance on methods such as hydrofracturing, there is an increased need for capacity to reliably contain gas within a formation and prevent ingress into inappropriate regions.
It is therefore an object of the present invention to provide a method of limiting or reducing permeability of a matrix to limit or reduce liquid and/or gas inflow, including limiting or reducing gas and/or liquid inflow within a passage in the matrix that reduces the aforementioned problems experienced with prior art methods.